Commonly, in the manufacturing of Light Emitting Device, LED phosphors are deposited over active light emitters in a powder or liquid suspension. To improve phosphor uniformity and simplify wafer, chip scale, or flip chip manufacture, phosphors distributed in a light transparent ceramic have also been developed. Such ceramics can be formed as plates (or platelets) with a controlled amount of phosphor powder being placed in a mold and heated under pressure to sinter the grains together. The platelet can be made very smooth on all surfaces, suitable for attachment.
One example of a ceramic platelet is Lumiramic™. Lumiramic is a phosphor platelet formed from polycrystalline ceramic plate of Ce (III) doped yttrium gadolinium aluminum garnet (Y,GdAG:Ce). The technical properties of Lumiramic are described in “Lumiramic: a new phosphor technology for high performance solid state light sources” (Bechtel, Helmut, Peter Schmidt, Wolfgang Busselt, and Baby S. Schreinemacher. “Lumiramic: A New Phosphor Technology for High Performance Solid State Light Sources.” Eighth International Conference on Solid State Lighting (2008): n. pag. Online), which is hereby incorporated by reference.
In some applications, Lumiramic plates can be combined with a blue LED to produce white light in the range of 5000 K correlated color temperature. In one automotive application, a Lumiramic platelet is glued to a blue LED using a silicone polymer glue that allows for heat conduction from the phosphor layer into the LED and heat sink as well as providing optical coupling of blue light into the Lumiramic plate to form white light. In other applications, a light emitting element is bonded to the Lumiramic plate using a surface activated bonding technique that relies on sputter etching with ion beams or plasma on a bonding surface of a light emitting element.
A bonding technique that does not require adhesives is atomic layer deposition (ALD). Atomic Layer Deposition (ALD) is a process in which a thin film deposition method in which a film is grown on a substrate by exposing its surface to alternate precursor gases. Methods for performing ALD are known in the art and for example are taught in “Atomic layer deposition (ALD): from precursors to thin film structures” (Leskeia, Markku, and Mikko Ritala. “Atomic Layer Deposition (ALD): From Precursors to Thin Film Structures.” Thin Solid Films 409.1 (2002): 138-46. Print), which is hereby incorporated herein by reference.